1. Field of the Invention
This invention relates to doors for pets, for example a door to allow the pets egress from or entry into a dwelling.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98
Pet doors of various kinds for cats and dogs are widely available. The doors for cats are usually called “cat flaps”.
Pet doors are adapted to be fitted in a lower portion of a wall or of an existing full-sized door. The pet door may consist simply of a flap, often being transparent so that the animal can see where it is going, and being hung from a horizontal axis to swing against the force of gravity when pushed by an animal. Alternative structures are mounted to swing about a vertical axis, but since they do not have gravity to bring the door/flap back to a closed position, they require springs to bias the door/flap to its neutral closed position. Also available are flexible transparent flaps, where the top of the flexible flap is held in fixed position and the animal bends the flap to make an entry or exit.
A simple latch may be provided for holding the door/flap at its neutral closed position so as to prevent movement of the door/flap in either direction or in just one direction. In the latter case, the latch may be arranged so as to allow entry but not egress or alternatively to allow egress but not entry.
The problem with such simple constructions is that, depending upon the position of the latch, any animal of the size to fit through the opening may gain entry or egress. In order to prevent passage of unwanted stray animals, pet doors have been designed with magnetically operable latches. The latch, powered by battery, is operable only when a magnetic tag (or in other operations an electrical loop) is detected. In simple mechanisms, any magnetic tag of adequate field strength will unlock the latch.
More sophisticated constructions have been designed in an attempt to allow selective operation of a door by a selected animal with the appropriate tag.
Pets commonly carry a subdermal identification coded tag. GB2376977 of Duerden, suggests transmitting a radio frequency signal at intervals to cause a signal to be transmitted by the standard passive coded subdermal identification tag carried by an animal, detection by a pet door of the retransmitted signal being adapted to open a pet door latch if the identification tag matches a code in memory. It is doubtful whether the Patentee had given any serious thought as to how the system could be put into effect. This prior proposal gives no detail as to how to effectively couple a transmitter or receiver at the pet door to a passive subdermal tag so as to get any useful received signal or how to discriminate between the millions of such tags in existence. In practice such subdermal tags can only be “read” by an interrogation coil placed on the skin immediately above the subdermal tag. If the tag has moved, in general it cannot be located. The poor coupling between an aerial associated with a pet door and the conventional subdermal tag, as well as the high energy requirements for a system based on utilizing such tags to control a pet door, makes a system of the kind proposed in GB2376977 unworkable.
GB1187383 of National Research Development Corporation is concerned with a somewhat different use, namely controlling access to different feeding spaces in a cow byre for different cows, in which each cow has a tag with a characteristic frequency effective to allow access only to its dedicated feeding space.